1. Field of the Invention
The present invention relates to a local time adjusting method of a mobile communication terminal and, more particularly, to a local time adjusting method of a mobile communication terminal capable of extending accuracy for a local time offset by the mobile communication terminal itself.
2. Description of the Background Art
In general, in a mobile communication, a CDMA (Code Division Multiple Access) terminal calculates a local time of an area where the CDMA terminal itself is positioned upon receiving a synchronous channel message from a base station through a sync channel.
Table 1 illustrates a data structure of a CDMA standard synchronous channel message, including a protocol version (P_REV) field provided for service in a current system, a system time (SYS_TIME) related to time, leap seconds (LP_SEC), an offset of local time (LTM_OFF), a daylight savings time (DAYLT), or the like.
TABLE 1FieldLength (bits)P_REV8. . .. . .SYS_TIME36LP_SEC8LTM_OFF6DAYLT1. . .. . .
The system time (SYS_TIME) is synchronized with a UTC (Coordinated Universal Time), and corresponds to a GPS (Global Position System) time counted in units of 80 ms based upon zero seconds, zero minutes and zero hours, Jan. 6, 1980.
The offset of local time (LTM_OFF), which means a GMT (Greenwich Mean Time) correction value (offset value) of a corresponding area, is counted 1 by 1 in units of 30 minutes and indicated as a complement of ‘2’ of 6 bits. At this time, a range that can be adjusted by 6 bits are 32 to 31, Which equivalent to −16˜+15 hours and 30 minutes when calculated by the unit of 30 minutes.
For instance, LTM_OFF of Kansas City in the United States is 110100 (6 bits, complement of ‘2’), which is equivalent to 12 as a decimal. Since 110100 is a value obtained by counting 1 for every 30 minutes, so that, actually, it is −6 hours. Namely, the LTM_OFF of the Kansas City is GMT −6:00.
The daylight savings time indicator (DAYLT) is ‘1’ if the daylight savings time is valid, and ‘0’ if the daylight savings time is not valid.
The local time in accordance with a related art is calculated by extracting time-related data from the sync channel and substituting it to equation (1) shown below:local time=SYS_TIME-(LP-SEC*12.5)+(LTM_OFF*22500)  (1)wherein ‘12.5’ is a count value (1 sec/80×10-3 sec) used for coordinating 1 second in units of 80 ms, and ‘25000’ is a count value used for coordinating 30 minutes (0.5 hour) in units of 80 ms.
A local time calculated by equation (1) is a value obtained by counting time by the unit of 80 ms starting from 0 seconds, 0 minutes and 0 hours, Jan. 6, 1980 in a corresponding area, and a mobile communication terminal outputs the present time at a present location (of the user) on a display unit by applying the local time.
As mentioned above, most countries adjusts a local time by the unit of 30 minutes on the basis of the GMT, but in some areas of Nepal (GMT+5:45) or New Zealand, a difference by the unit of 15 minutes, not 30 minutes, is made over the GMT.
Namely, in the local time adjusting method of a mobile communication terminal, the local time is calculated by using a value of the LTM_OFF field counted in units of 30 minutes, so that for a mobile communication terminal in an area, such Nepal (GMT+5.45), where 15 minutes of difference is made over the GMT, a difference of a maximum −15 minutes (in case of GMT+5.30) or +15 minutes (in case of GMT+6:00) compared to actual local time is made.
In addition, in order to solve the above problems, existing CDMA standards should be changed to change the value of the LTM_OFF field to a value of 7 bits in units of 15 minutes. Then, changing of the CDMA standards should accompany change of all the mobile communication systems.